1. Field of the Invention
The present invention relates generally to an assembly that allows for the flexible location of an optical device within an optical communications network, and more specifically to a retractable optical fiber tether assembly and the associated fiber optic cable. In one exemplary application, a plurality of these retractable optical fiber tether assemblies are used to flexibly deploy an antenna array for a wireless local area network (WLAN) or the like, the associated fiber optic cable carrying both optical fiber to provide optical continuity and copper wire to provide electrical conductivity to the antenna array.
2. Technical Background of the Invention
In various applications, it is desirable to flexibly locate an optical device that is coupled to a patch panel in a wiring closet or other optical signal source through a series of fiber optic cables and optical connections, or to flexibly locate an array of such optical devices. For example, on a campus or in an office building, multiple-dwelling unit (MDU), single dwelling, etc., it is often desirable to flexibly locate an optical connector or port, a flexible network access point (FlexNap—Corning Incorporated), or the like in each building, office suite, office, unit, room, etc. As used herein, the terms “flexible,” “flexibly,” and “flexibility” refer to the ability to select the end location of the optical connector or port, FlexNap, or the like without significant constraint caused by the fixed length of the terminating portion of the cable (i.e. the tether or drop cable) or the placement of the originating or intervening portions of the cable (i.e. the tail cable or array cable).
In a conventional installation, the tail cable optically couples the patch panel in the wiring closet or other optical signal source to multiple optical connectors at a different location. For example, in an office building, the patch panel may be located in a wiring closet in the basement or on the ground floor and the optical connectors may be on a higher floor having multiple office suites. The array cable optically couples the optical connectors to multiple tether cables at multiple access points, such as multiple FlexNaps or the like. In the office building, the array cable may run through the wall or ceiling of a hall connecting the office suites, an access point associated with each of the office suites. The tether cables, which are preferably pre-connectorized, then bring the optical signal into each of the office suites. Disadvantageously, the tether cables typically each have a fixed length, dictating the end locations of the optical connectors or ports, FlexNaps, or the like, or requiring that excess tether cable be neatly coiled in each of the office suites. Thus, what is needed in the art is an optical system that incorporates one or more retractable optical fiber tether assemblies, providing the desired location flexibility and obviating the need for neatly coiling the tether cable, such that an array of optical devices may be installed with minimal effort and expense.
What is also needed in the art is an optical system that incorporates one or more retractable optical fiber tether assemblies, such that an antenna array for a WLAN or the like may be flexibly deployed. In such an application, the associated fiber optic cable must carry both optical fiber to provide optical continuity and copper wire to provide electrical conductivity to the antenna array. Optical fiber and copper wire are carried separately in existing solutions.
One approach to deploying a wireless communications system involves the use of “picocells,” which are radio-frequency (RF) coverage areas having a radius in the range of about a few meters up to about 20 meters. Because a picocell covers a small area, there are typically only a few users (clients) per picocell. Picocells also allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.
In conventional wireless communications systems, picocells are created by and centered on a wireless access point device connected to a head-end controller. The wireless access point device includes digital information processing electronics, an RF transmitter/receiver (transceiver), and an antenna operably connected to the RF transceiver. The size of a given picocell is determined by the amount of RF power transmitted by the access point device, the transceiver sensitivity, the antenna gain, and the RF environment, as well as by the RF transceiver sensitivity of the wireless client device. Wireless client devices typically have a fixed RF transceiver sensitivity, so that the above-referenced properties of the access point device mainly determine the picocell size. Combining a number of access point devices connected to the head-end controller creates an array of picocells that cover an area called a “picocellular coverage area.” A closely packed picocell array provides high per-user data throughput over the picocellular coverage area.
Conventional wireless systems and networks are wire-based signal distribution systems where the access point devices are treated as separate processing units linked to a central location. This makes the wireless system/network relatively complex and difficult to scale, particularly when many picocells need to cover a large region. Further, the digital information processing performed at the access point devices requires that these devices be activated and controlled by the head-end controller, which further complicates the distribution and use of numerous access point devices to produce a large picocellular coverage area.
While radio-over-fiber (RoF) wireless picocellular systems are generally robust, there are some limitations. One limitation relates to the radiation pattern from the transceiver antenna. Though microstrip antennas have a directional radiation pattern, they are generally more expensive and more complicated to integrate into a RoF cable than the simpler and less expensive dipole antennas. However, dipole antennas in the form of wires radiate omnidirectionally in a plane perpendicular to the RoF cable. This wastes energy and also interferes with other picocells, such as those formed in the floor above the ceiling in which the RoF cable is deployed.
Another limitation relates to the need for having a transceiver for each picocell. The typical RoF transceiver includes a mechanical housing, a laser, a photodetector, a printed circuit board with RF electronics, optical connectors, and electrical connectors. The relatively small size of picocells typically requires that the transceivers be spaced apart by between about 5 to 10 meters or so. A RoF wireless picocellular system would be easier to deploy and be less expensive if the number of transceivers could be reduced.
A further limitation relates to locating RoF transceivers after they are deployed. The typical RoF wireless picocellular system includes one or more RoF cables that are hidden in a building's infrastructure, such as above a suspended ceiling. This makes it difficult for service personnel to locate a problematic transceiver. One way of deploying transceivers is to tether them to respective access points in the RoF cable using a tether cable. However, the position of each transceiver relative to the RoF cable tends to be different, requiring different lengths of tether cable. This requires that the slack in some of the tether cables be addressed by coiling the tether or otherwise storing the excess tether cable. In addition, tether cabling needs to be packaged for shipping in a manner that lends itself to ease of installation since quicker system installation translates into cost savings.